The phenotype of rotund (rn) null alleles is described, and compared to wild type. The mutants are expressed zygotically and cause position specific defects in certain imaginal discs (antenna, legs, wing, haltere and proboscis) and their corresponding adult derivatives. In the discs, specific folds are absent in rn mutants compared to wild type. Clonal analysis shows that the rn (+) gene is partially autonomous in its expression in cells destined to form certain distal parts of the adult appendages. The results are consistent with the idea that the rn (+) gene is required for normal morphogenesis of specific distal parts of the adult appendages.